1. Field of the Invention
The present invention relates to a light emitting diode lamp including a light emitting element packaged with a molded portion made of a transparent synthetic resin.
2. Description of the Related Arts
JP-A 1-152676 and JP-U 62-44530, for example, disclose a light emitting diode lamp of the type described above. Such a light emitting diode lamp generally includes a pair of lead terminals one of which has a front end formed with a cup in the form of an inverted truncated cone. The cup has a conical inner circumferential surface which is made a light reflective surface and a bottom surface on which an LED chip is bonded. The LED chip is connected to the other terminal by wire bonding using a thin metal wire. These elements are packaged by a molded portion made of a transparent synthetic resin and having a lens portion.
Specifically, as shown in FIG. 24 which shows the principal portion as enlarged, such a prior art light emitting diode lamp includes an LED chip 104 including an active light emitting layer 104a interposed between a lower layer 104b and an upper layer 104c. The LED chip 104 is bonded, with a die bonding material H, to a flat bottom surface 108b of a cup 108 formed as a recess at a front end of one lead terminal 102. The inner circumferential surface of the cup 108 is made a conical light reflective surface 108a, so that the light emitted from the light emitting layer 104a of the LED chip 104 is reflected upward in the figure by the conical light reflective surface 108a of the cup 108.
As shown in FIG. 25, conventionally, in bonding the LED chip 104, an appropriate amount of thermally meltable die bonding material H (i.e., a material that melts when heated and hardens when cooled) such as solder paste or a thermally hardenable die bonding material (i.e., a material that hardens when heated) is applied to the bottom surface 108b of the cup. Then, after the LED chip 104 is placed on the applied die bonding material H, the die bonding material is melted by heating and then hardened (or hardened by heating when a thermally hardenable die bonding material H is used).
However, since the bottom surface 108b of the cup 108 is a flat surface which is perpendicular to an axis 108c of the cup 108, the distance of the LED chip 104 from the bottom surface 108b varies depending on the amount of the die bonding material H applied to the bottom surface 108b. In other words, the height of the LED chip 104 varies along the axis 108c of the conical reflective surface 108a of the cup 108 depending on the applied amount of the die bonding material H. Therefore, the accuracy in positioning the LED chip 104 at a predetermined height position along the axis of the conical light reflective surface 108a of the cup 108 is low, which leads to a deterioration of conversion of light by the cup 108.
Further, when a large amount of die bonding material H is applied, the LED chip 104 placed thereon may be bonded while being inclined relative to the axis 108c of the cup 108. Also in such a case, the conversion of light by the cup is deteriorated.
In some cases, the light emitting layer 104a of the LED chip 104 is provided closer to the bottom surface (P layer) of the LED chip 104. Generally, in this type of LED chip, the light emitting layer 104a is positioned at a height of about 5 μm above the bottom surface of the LED chip 104.
When the LED chip 104 in which the light emitting layer 104a is arranged close to the bottom surface of the LED chip is placed on the thermally meltable die bonding material H applied to the bottom surface 108b of the cup 108 and heating is performed, the molten die bonding material H, if the amount is large, rises from the bottom surface (lower layer 104b) onto the side surface or is bulged to reach the upper layer 104c over the light emitting layer 104a and then hardens in such a state (See FIG. 24). In such a case, short circuiting between the lower layer 104c and the upper layer 104c may occur to cause a failure. Further, since the thermally meltable or thermally hardenable die bonding material H pushed out from under the bottom surface of the LED chip 104 and bulged to a position higher than the light emitting layer 104a is hardened without contacting the outer side surface of the LED chip 104, the light emitted from the light emitting layer 104a is blocked by the bulged die bonding material H. In this way, since the peripheral surface of the light emitting layer 104a is in such a covered state with the die bonding material H, the light cannot reach the conical light reflective surface 108a of the cup 108, whereby the light emission efficiency is considerably deteriorated.
When the thermally meltable die bonding material H applied to the bottom surface 108b in the cup 108 is melted by heating, the die bonding material flows along the flat bottom surface 108b of the cup 108 to spread onto all sides. Therefore, the LED chip 104 on the molten die bonding material H moves horizontally along the bottom surface 108b to be away from the axis 108c due to the spreading of the die bonding material H to all sides. Thus, when the die bonding material H is hardened, the LED chip is fixed to such a deviated position.
In this way, in bonding the LED chip 104 to the bottom surface 108b of the cup 108 in the prior art structure, the LED chip 104 deviates horizontally relative to the axis 108c of the cup 108 due to the spreading of the thermally meltable die bonding material H to all sides upon heating. Thus, it is difficult to accurately position the center of the LED chip 104 on the axis 108c of the cup 108 or the nearby position, so that the conversion of light by the cup is deteriorated.